Vision Eye is the window to our soul

Vision How does the eye work Phototransduction: conversion of light energy turns into neural messages http://www.youtube.com/watch?v=JadaWSDxBYk

What makes up a light wave?

The Stimulus Input: Light Energy Visible Spectrum Both Photos: Thomas Eisner

3 Characteristics of Light Wavelength (hue/color) Intensity (brightness) Saturation (purity)

Wavelength The distance from the peak of one light wave to the peak of the next. The distance determines the hue (color) of the light we perceive.

ROYGBIV

Intensity The amount of energy in a light wave. Determined by the height of the wave. The higher the wave the more intense the light is.

Intensity (Brightness) Intensity Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

Purity (Saturation) Monochromatic light added to green and red Saturated Saturated Monochromatic light added to green and red makes them less saturated. https://www.youtube.com/watch?v=l8_fZPHasdo

Color Vision Two Major Theories

Trichromatic Theory Three types of cones: Red Blue Green These three types of cones can make millions of combinations of colors. Does not explain afterimages or color blindness well.

Visual Information Processing Opponent-Process Theory- opposing retinal processes enable color vision “ON” “OFF” red green green red blue yellow yellow blue black white white black

Opponent Process Theory Hering proposed that we process four primary colors combined in pairs of red-green, blue-yellow, and black-white. Cones Retinal Ganglion Cells

Opponent-Process theory The sensory receptors come in pairs. Red/Green Yellow/Blue Black/white If one color is stimulated, the other is inhibited.

Opponent Processing Theory Does this make your eyes all weird out??

Sensation & Perception 5/14/2019 Opponent Process- Afterimage Effect They are caused by fatigued cells in the retina responding to light. After image: Stare at this picture for around 30 seconds. If you look away from the computer monitor and stare at the wall, do you see an after image on the wall? Figure 3.10 from: Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall. Psychology, 4/e by Saul Kassin ©2004 Prentice Hall ©2001 Prentice Hall

Opponent processing theory: we see in pairs

Cones and Rods

Retina’s Reaction to Light Receptors Rods concentrated in periphery approx. 120 million detect black, white and gray twilight or low light Cones Concentrated near center of eye (fovea) fine detail and color vision daylight or well-lit conditions approx. 6 million Blind Spot- region with NO rods or cones http://dragon.uml.edu/psych/bspot.html

Parts of the eye Cornea: Transparent tissue where light enters the eye. (COVERS get it Cornea) Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light. Lens: Focuses the light rays on the retina. Retina: Contains sensory receptors that process visual information and sends it to the brain.

The Lens Lens: Transparent structure behind the pupil that changes shape to focus images on the retina. Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

Nearsighted Vision

Farsighted Vision

Bipolar cells in the first layer translate the information from rods and cones back out to the ganglion cells.  Ganglion cells then transfer the information down toward the optic nerve. The point where the optic nerve exits the eye is a blind spot. You cannot see anything because there are no photo-receptors at the point at which those cells exit the retina. The information is carried down the optic nerve, where it undergoes additional processing. Color information is added at the thalamus. At the end of the optic nerve is the occipital lobe, the structure most responsible for visual processing.

Optic Nerve, Blind Spot & Fovea Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. This creates a blind spot. Fovea: Central point in the retina around which the eye’s cones cluster. http://www.bergen.org

The Retina

Test your Blind Spot Use your textbook (p. 207). Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At some point the car on the right will disappear due to a blind spot. lab

Binocular Cues We need both of our eyes to use these cues. Retinal Disparity (as an object comes closer to us, the differences in images between our eyes becomes greater. Convergence (as an object comes closer our eyes have to come together to keep focused on the object).

Visual Information Processing Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex. OBJECTIVE 7| Discuss the different levels of processing that occur as information travels from the retina to the brain’s cortex.

Feature Detection Cells Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement. Ross Kinnaird/ Allsport/ Getty Images Hubel and Wiesel received a Nobel Prize for their work on Feature Detectors. These specialized nerons in the occipital lobe’s visual cortex receive information from individual ganglion cells in the retina. https://www.youtube.com/watch?v=y_l4kQ5wjiw

Visual Information Processing Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form and movement etc. OBJECTIVE 8| Discuss parallel processing and discuss its role in visual processing.

Color Stitch is anything but blue. Stitch rejects the wavelengths of light that to us are blue- so blue is reflected of and we see it. Also, light has no real color. It is our mind that perceives the color.

Color Blindness Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory. Ishihara Test

Color Blindness Simulators Check out these sites to see what a color blind person sees (normal, red blind, blue blind, monochromatic) http://www.colblindor.com/coblis-color-blindness-simulator/ http://www.webexhibits.org/causesofcolor/2.html

Color Constancy Color of an object remains the same under different illuminations. However, when context changes the color of an object may look different. OBJECTIVE 10| Explain the importance of color constancy. R. Beau Lotto at University College, London